Axial-flow fan having inner and outer blades

ABSTRACT

There is provided an axial-flow fan which is capable of producing axial-flow wind near the outer circumference of a fan clutch to extend the functional life of the fan clutch, and which is capable of decreasing the inertia moment of an engine cooling plastic fan and hence vibration loads to be transmitted to the bearing of the fan clutch, thereby extending the structural life of the fan clutch and increasing the burst speed of the engine cooling plastic fan. The axial-flow fan includes an inner plastic hub, plural inner plastic blades each of which extends radially from the inner plastic hub and is twisted near its extending end and connected to a portion immediately below the base of the corresponding one of the outside blades, an outer plastic hub connected to the plural inner plastic blades, and plural outer plastic blades which extend radially from the outer plastic hub.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an improved structure of an engine-driven type of axial-flow plastic cooling fan to be used for cooling an internal combustion engine for an automobile or a similar engine and, more particularly, to an synthetic-resin-made engine cooling fan which has a reinforced structure made of a hub and fan blades formed as an integral component and is driven mainly via a fan clutch, and which is improved in the performance of cooling the fan clutch.

[0003] 2. Description of the Prior Arts

[0004] This kind of engine cooling fan has heretofore been divided into two major structure types of axial-flow plastic fans. Either of these types of plastic fans has a circular steel insert for fitting a fan to a fan clutch fitted to the shaft of a water pump. FIGS. 5 and 6 respectively illustrate the states where the two prior art major structure types of axial-flow fans are fitted to fan clutches. In the axial-flow plastic fan shown in FIG. 5, a circular steel insert 20 having a locking hole 21 in its outer circumferential portion is bent by 90° near the outer circumferential portion, and that bent portion is embedded in a plastic hub 22 which has a structure integral with a fan blade 23. In the axial-flow plastic fan shown in FIG. 6, a circular steel insert 30 which does not have a bent portion but has a locking hole 31 in its outer circumferential portion is embedded in a plastic hub 32 which has a structure integral with a fan blade 33 in a similar manner to the plastic hub 22. The respective axial-flow plastic fans shown in FIGS. 5 and 6 are fitted to fan clutches 24 and 34.

[0005] The respective axial-flow plastic fans shown in FIGS. 5 and 6 have structures in which the steel inserts 20 and 30 extend into the plastic hubs 22 and 32. Plastics are respectively injection-molded together with the steel inserts 20 and 30 so that the steel inserts 20 and 30 are respectively embedded into the plastic hubs 22 and 32, and the plastics are charged into the locking holes 21 and 31, thereby providing full adhesion or connection between the steel insert 20 and the plastic hub 22 as well as between the steel insert 30 and the plastic hub 32. Each of these two types of fans serves as an engine cooling fan for an internal combustion engine which has a cylindrical hub and plural fan blades radially disposed on the outer circumferential wall of the cylindrical hub with the cylindrical hub and the plural blades being integrally formed by injection molding with plastics. Both of the prior art structures only have one hub and outside plastic blades.

[0006] In general, engine cooling fans are subjected to the influence of hard vibrations of engines during high-speed rotations thereof in particular. For this reason, the engine cooling fans are repetitively subjected to the influences of not only vibrations of engines but also resonance phenomena caused by nonuniform aerodynamic loads due to the complicated and nonuniform shapes of the lower hoods of automobiles. Moreover, such an engine cooling fan is also subjected to vibration loads due to the deviation between the axis of a water pump and the axis of the fan as well as the static unbalance of the fan which causes the dynamic unbalance thereof during high-speed rotation. Since the engine cooling fan is driven via a fan clutch, the vibration force of the fan is transmitted to the bearing of the fan clutch. As the mass and the inertia moment of the fan are larger, the force to be transmitted to the bearing of the fan clutch is larger. If large vibration loads are repetitively applied to the bearing of the fan clutch, fatigue and other damages occur in the bearing. There has been, therefore, the risk that the prior art engine cooling fans give structural damage to the fan bearings of fan clutches.

[0007] There are many cases where another problem of a viscous fan clutch which drives a prior-art general axial-flow plastic fan gives rise to degradation of the silicone oil of the fan clutch which drives the engine cooling fan with high viscosity. High shearing stress which occurs in the silicon oil owing to a slip between the engine cooling fan and the fan clutch generates heat which causes the temperature of the silicone oil to rise to an extent exceeding 170° C. If this viscous silicone oil is exposed to such a high temperature, the characteristics of the silicone oil change and the viscosity retention of the silicone oil decreases with time. As a result, the malfunction of the fan clutch occurs. To avoid this malfunction, it is necessary to improve the capability to cool the clutch.

[0008] However, the structure of the prior art axial-flow fans shown in each of FIGS. 5 and 6 has the problem that air flows near the outer circumference of the fan clutch circulate in the axial direction (axial flow) and cannot reach an engine side by the planer steel inserts 20 and 30 of major diameter of a internal hub, so that the fan clutch cannot be fully cooled. Either of such prior art fans has a large steel insert and hence the problem that the inertia moment of the plastic fan increases. As a result, since loads to be transmitted to the bearing of the fan clutch in a vibrating state increase, the life of the bearing of the fan clutch becomes short, so that there is a possibility that the structural life of the fan clutch becomes short.

SUMMARY OF THE INVENTION

[0009] The invention has been made to solve the above-described problems of the prior art cooling fans, and provides an axial-flow fan which is capable of producing forced axial-flow cooling air for a fan clutch to extend the functional life of the fan clutch, and which is capable of decreasing the inertia moment of an engine cooling plastic fan and hence vibration loads to be transmitted to the bearing of the fan clutch, thereby extending the structural life of the fan clutch and increasing the burst speed of the engine cooling plastic fan.

[0010] The gist of the invention resides in an axial-flow fan fitted to an output shaft of an internal combustion engine and provided with inner and outer blades, which includes an inner plastic hub in which a steel insert is embedded as required, plural inner plastic blades each of which extends radially from the inner plastic hub and has a base side (the vicinity of a root portion) approximately parallel to a plane perpendicular to the rotational axis so as not to interfere with the case of a fan clutch and is twisted near its extending end and connected to a portion immediately below the base of the corresponding one of the outside plastic blades, an outer plastic hub connected to the plural inner plastic blades, and plural outer plastic hubs which extend radially from the outer plastic hub.

[0011] In accordance with a particular structure according to the invention, the bases of the outer blades near the plastic-made outer hub extend inwardly and meet another hub having a small circumference (the inner plastic hub). Since the outer fan blades further radially inwardly from the lower outer hub and meet the inner hub, the radially extending portions of the respective blades constitute the inner blades. Incidentally, a circular steel insert having holes in its outer circumferential portion may be embedded into the inner hub after being bent by 90°.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The invention will become more readily appreciated and understood from the following detailed description of a preferred embodiment of the invention when taken in conjunction with the accompanying drawings, in which:

[0013]FIG. 1 is a perspective conceptual view showing one embodiment of an axial-flow fan according to the invention;

[0014]FIG. 2 is a perspective conceptual view, partly broken away, showing part of the axial-flow fan shown in FIG. 1;

[0015]FIG. 3 is an enlarged cross-sectional view taken along line III-III of FIG. 1;

[0016]FIG. 4 is an enlarged cross-sectional view taken along line IV-IV of FIG. 1;

[0017]FIG. 5 is a cross-sectional conceptual view showing part of a prior art axial-flow fan; and

[0018]FIG. 6 is a cross-sectional conceptual view showing part of another prior art axial-flow fan.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0019] In a preferred embodiment of the invention, reference numeral 1 denotes an inner plastic hub, reference numeral 2 an inner plastic blade, reference numeral 3 an outer plastic hub, reference numeral 4 an outer plastic blade and reference numeral 5 a steel insert.

[0020] An axial-flow fan provided with inner and outer blades according to the invention includes the inner plastic hub 1 in which the small circular steel insert 5 having locking holes 5-1 in its outer circumferential portion is embedded, the plural inner plastic blades 2 each of which has a flat portion 2-1 and a twisted portion 2-2 formed near the flat portion 2-1 and is connected to a portion immediately below the base of the corresponding one of the outside plastic blades 4, the flat portion 2-1 extending radially from the inner plastic hub 1 and being approximately parallel to a plane perpendicular to the rotational axis so as not to interfere with a fan clutch, and the outer plastic hub 3. The steel insert 5 is injection-molded together with the plastic fan.

[0021] The main feature of the invention resides in the structure in which the inner plastic hub 1 and the outer plastic hub 3 are connected to each other by the inner plastic blades 2 each having the flat portion 2-1 and the twisted portion 2-2 and the twisted portion 2-2 of each of the inner plastic blades 2 is disposed immediately below the base of the corresponding one of the outer plastic blades 4.

[0022] Specifically, in the invention, wind which is indicated by an arrow F in FIG. 4 is produced by the inner plastic blades 2 between the inner plastic hub 1 and the outer plastic hub 3, and this wind flows through the spaces between fins which are radially disposed on a fan clutch, thereby effecting additional cooling of the fan clutch. The front end of the front side of each of the fan and the fan clutch faces ram air which flows into a lower hood of a vehicle. When the ram air flows into the fan, the outer plastic blades 4 suck the inflow air and send the air toward an engine block. At this time, since the fan is rotating, part of the air passes through the spaces between the inner plastic blades 2 by the fin action (blade action) of the twisted portions 2-2 between the inner plastic hub 1 and the outer plastic hub 3, thereby forcedly changing air surrounding the fan clutch into an axial flow to cool the fan clutch. The upper limit of the maximum temperature of the silicone oil inside the fan clutch that allows the fan clutch to operate safely for a long time is about 170° C., and therefore, if the temperature of the silicone oil is lowered by 2-3° C., the durability and the life of the fan clutch can be improved to a great extent.

[0023] Accordingly, the axial-flow fan provided with the inner and outer blades according to the invention can improve air flows surrounding the fan clutch and hence extend the functional durability of the fan clutch.

[0024] In addition, in the invention, each of the inner plastic blades 2 between the inner plastic hub 1 and the outer plastic hub 3 is twisted at its extending end portion and reaches the portion immediately below the base of the corresponding one of the outer plastic blades 4, and the outer plastic hub 3 is disposed at a position where the respective extending ends of the inner plastic blades 2 and the bases of the outer plastic blades 4. In other words, since the respective twisted portions 2-2 are formed near the extending ends of the inner plastic blades 2, stresses occurring due to centrifugal loads decrease. Repetitive loads imposed on the fan produces fatigue in which the torsion moments and tensile forces of the fan blades are combined. One experiment which is generally carried out in the automobile industry in order to examine the maximum strength of a fan is to rotate an engine-cooling plastic fan until it is broken, and record the maximum rpm of the fan. The fan structure according to the invention is slightly high in “burst rpm” when compared with the prior art fan structures. Accordingly, the fan according to the invention has a mechanical strength approximately equal to or greater than those of the prior art fans.

[0025] Moreover, in the invention, the inner plastic hub 1 and the inner plastic blades 2 are formed integrally with the outer plastic hub 3 and the outer plastic blades 4 by injection molding. The inner plastic hub 1, the inner plastic blades 2, the outer plastic hub 3 and the outer plastic blades 4 are all made of synthetic resin, and the inertial moment of the fan is smaller than that of the prior art engine cooling fan which only uses the steel-made large-diameter insert 20 and the synthetic-resin-made outer plastic hub 22 and outer plastic blades 23. In this manner, as the inertial moment of the fan decreases, inertial load decreases compared to the prior art engine cooling fan which uses the large steel insert. In the case of the prior art engine cooling fan, a large inertial load occurs during vibration and there is the risk of structural destruction of the bearing. However, in the case of the axial-flow fan according to the invention, since the inertial moment decreases, the magnitude of vibration load to be applied to the bearing decreases, whereby the fatigue life of the bearing of the fan clutch is extended.

[0026] As described above, the axial-flow fan provided with the inner and outer blades according to the invention can improve air flows surrounding the fan clutch and hence extend the functional durability of the fan clutch. In addition, as compared with the prior art fan structures, the fan structure according to the invention is slightly high in “burst rpm”, whereby the fan according to the invention can be given a mechanical strength approximately equal to or greater than those of the prior art fans. Moreover, since the inertial moment of the fan decreases, inertial load decreases compared to the prior art engine cooling fan which uses the large steel insert, and the magnitude of vibration load to be applied to the bearing decreases, whereby it is possible to achieve a superior advantage such as an extension of the fatigue life of the bearing of the fan clutch.

EXAMPLES

[0027] The results of the experiments performed as to the air flow of an axial-flow fan according to the invention and that of a prior art axial-flow fan are shown below.

[0028] (a) Experiment as to Air Flow

[0029] Two fans each having eleven blades and the same dimensions such as an outer diameter of 490 mm, an outer boss diameter of 238 mm and a blade width of 50 mm were selected for the experiment. One of the two fans was a fan according to the invention, and the other was a prior art fan of the type shown in FIG. 5 which had the same diameter and hub diameter. The second fan is a prior art fan. The maximum temperature occurring inside a clutch is determined by the movement of air surrounding the clutch. As the air moves faster, the maximum temperature becomes lower. As the experiment, constant-temperature measurements were performed in a room at room temperature with 500 rpm and 1,000 rpm. The results are shown in Table 1 (the fan according to the invention) and Table 2 (the prior art fan). Incidentally, the measurement positions are positions which correspond to the radial positions of the twisted portions 2-2 of the blades and are immediately before an outer boss portion.

[0030] From the data of Tables 1 and 2, it is seen that the fan, according to the invention, produces a speed more than twice as fast as that is observed with the prior art fan. TABLE 1 Speed with Fan according to the Invention DIRECTION 500 rpm 1,000 rpm AXIAL DIRECTION 2.3 m/s 4.8 m/s

[0031] TABLE 2 Speed with Prior Art Fan DIRECTION 500 rpm 1,000 rpm AXIAL DIRECTION 1.1 m/s 1.8 m/s

[0032] (b) Temperature of Fan Clutch

[0033] <Condition>

[0034] Experiments were performed as to a prior art fan and a fan having inner and outer blades according to the invention, and the temperatures of the outer circumferential surfaces of the bearing outer races of their respective fun clutches were measured through their embedded thermocouples. The use conditions were: diameter of clutch disk—132 mm; room temperature—90° C.; input speed—4,000 rpm; and fan speed—2,850 rpm.

[0035] <Result>

[0036] The measurements performed as to the prior art fan and the fan according to the invention showed that the temperature of the outer circumferential surface of the bearing outer race of the prior art fan was 165° C., whereas that of the fan according to the invention decreased to 155° C. by about 10° C. In the case of the fan according to the invention, it is inferred that such temperature decrease is due to the fact that high-speed axial-flow wind occurs inward of the hub owing to the twisted portions of the inner blades. 

1. An axial-flow fan fitted to an output shaft of an internal combustion engine and provided with inner and outer blades, comprising: an inner plastic hub; plural inner plastic blades each of which extends radially from the inner plastic hub and has a base side parallel to a plane of rotation and is twisted near its extending end and connected to a portion immediately below a base of the corresponding one of the outside blades; an outer plastic hub connected to the plural inner plastic blades; and plural outer plastic blades which extend radially from the outer plastic hub.
 2. An axial-flow fan provided with inner and outer blades according to claim 1, wherein a steel insert is embedded in the inner plastic hub. 